In recent years, an amount of information obtained by information appliances, such as car navigation systems and digital televisions, has been significantly increasing. For example, information, such as names of places and facilities in wider regions, is recorded in map databases referred by the car navigation systems. Furthermore, detailed program information of programs distributed through many channels, such as names of programs and cast members, is being distributed to electronic program guides (referred to as EPG hereinafter) for digital televisions. As interfaces for searching for such information, speech recognition techniques are notable.
However, the more the number of target words to be recognized increases, the lower the recognition ratio becomes in a speech recognition device. The speech recognition device is a device which stores, in a word dictionary, words, such as names of places, facilities, programs and cast members, and recognizes these words as target words. Furthermore, the speech recognition device obtains these target words via a communication means and stores them in a recognition dictionary. When the number of stored words reaches the maximum storage capacity of the recognition dictionary, there is a problem that it becomes impossible to obtain and store newly recognized words.
In order to solve such a problem, conventionally, various techniques have been suggested (for example, Patent References 1 and 2). FIG. 8 shows the configuration of the first conventional technique described in Patent Reference 1. The technique relates to a speech recognition device used in the operation of the EPG. As shown in FIG. 8, in the conventional speech recognition device, an EPG receiving unit 5 receives EPG data, and an item classifying unit 6 classifies the data into certain items. Then, a reading obtaining unit 7 refers to a kanji-to-kana conversion unit 15 and obtains the reading. Then, a dictionary updating unit 8 registers a pair of a word and the reading in a dictionary 9, and a registered word deleting unit 14 deletes the registered data, for example, the old data which has been registered by the preceding day. The words which newly appear in the EPG data (new programs and new cast members) are registered, and the items which have been registered and stored in the dictionary for a predetermined period of time are deleted. With such operations, it is possible to prevent the recognition ratio from being lowered due to the increase in the number of words stored in the recognition dictionary, and the amount of data stored in the dictionary from exceeding the limit and overflowing. Furthermore, it becomes possible to achieve the speech recognition processing using the dictionary in which the latest EPG data is reflected.
Furthermore, the second conventional technology described in Patent Reference 2 applies a speech recognition device for searching for names of places using a car navigation system installed in a vehicle. It has the configuration in which the names of places are recognized, using traffic information transmitted from traffic information transmitting units installed alongside roads (referred to as “beacons”). More specifically, a word indicating a name of a place in the vicinity of the vehicle (for example, a town name, an intersection name, road name, station name, a name of a structural object) is extracted, and such word is used as a target word to be recognized at the point in time. The traffic information transmitting unit provides detailed information of place names in the vicinity of a position where each of the unit is set. When the user moves by driving the vehicle and the current position of the user varies, the traffic information received by the traffic information transmitting unit is also updated to the one specifically for the vicinity of the current position. Then, the traffic information to be newly received by the traffic information transmitting unit includes place name information corresponding to the latest position information. With the aforementioned configuration, it is possible to achieve a speech recognition device which can prevent a recognition ratio of words from being lowered due to the increase in the number of words stored in a recognition dictionary and which can always recognize names of places in the vicinity of a current position as target words to be recognized.    Patent Reference 1: Japanese Laid-Open Patent Application No. 2001-22374    Patent Reference 2: Japanese Patent No. 3283359